Method and device for pneumatic feeding of materials

ABSTRACT

Method and device for pneumatic feeding of materials to be conveyed along a feeding line (10) supplied continually with conveying gas from conveying gas lines (18) discharging into the feeding line and spaced consecutively apart from each other. Each gas line (18) has at a distance from its opening (28) a short cross-sectional constriction (20), in the area of which the velocity of the conveying gas is increased to the velocity of sound and decreased again before the opening (28). A plurality of gas lines (18) are fed from a common supply line (16, 17) which runs adjacent to the feeding line (10). The gas lines (18) open into the feeding line (10) at an acute angle of approx. 35° and have two sections (21, 23) detachably connected with each other by a sealing screw connection (24), an apertured diaphragm, forming the cross-sectional constriction (20), and a filter (22) being held interchangeably by the screw connection.

The invention relates to a method and device for pneumatic feeding ofpowdery and/or granulated bulk materials, of heavy flowing and/orsticky, of abrasive, sensitive and/or moist materials in a tubularfeeding line by means of a device, the feeding line of which is suppliedwith carrier gas along its length from a plurality of gas linesdischarging into the feeding line and spaced consecutively apart fromeach other. It is therefore intended to provide a very advantageous,so-called seal flow feeding in respect of feeding capacity and economicefficiency (comparably lower energy requirements) in comparison withother pneumatic feeding methods.

A method of this type is known, for example, from DE-PS No. 26 57 677.This known method does, however, have the disadvantage that the carriergas from the pressure gas source, which supplies the gas linesdischarging into the feeding line, will, when a plug forms in thefeeding line, flow into the feeding line essentially through that gasline which offers least resistance. This leads to an uneven supply ofgas into the feeding line and there is also no chance of the plug in thefeeding line being dissolved.

In the case of another known feeding device (DE-PS No. 449 393) having agas supply line adjacent to the feeding line valves are disposed in thegas lines running from the gas supply line to the feeding line, thesevalves automatically opening and closing again to eliminate any plugsformed in the feeding line, i.e. with this known feeding device the gaslines discharging into the feeding line are normally closed. Thedisadvantage of this known feeding device is therefore not only that itdoes not work in accordance with the seal flow supply method mentionedbut that the pressure-responsive controllable valves in the gas linesrequire considerable resources and are also a source of possibleinterruptions.

The object of the present invention was therefore to develop a method ofthe type mentioned at the beginning such that even if plugs are formedin the feeding line selected amounts of gas may reach the feeding linethrough the individual gas lines and that plugs can be dissolved.

This object may be solved according to the invention in that thevelocity of the gas in each of the gas lines is increased to thevelocity of sound at a point before the opening into the feeding lineand likewise decreased again before the opening. By generating thevelocity of sound at a point in each of the gas lines the amount of gasflowing through each gas line per unit of time will be independent ofthe pressure ratio in the feeding line; decreasing the velocity of thegas before the opening into the feeding line prevents the wall of thefeeding line in the area where the gas lines open into it beingsubjected to intense erosive abrasion. The method according to theinvention may be carried out by a particularly simple device; based on afeeding device having a tubular feeding line, into which a plurality ofgas lines open, these being spaced consecutively apart from each otherand fed from at least one pressure gas source, such a device is designedaccording to the invention such that each gas line has at a distancefrom its opening into the feeding line a cross-sectional constriction,the throughflow cross section widening again between this constrictionand this opening, and that the pressure of the gas before thecross-sectional constriction is in over-critical ratio to the pressurein the feeding line. According to the invention no movable parts arerequired in the gas lines, in contrast to the known feeding deviceaccording to DE-PS No. 449 393, and the cross-sectional constriction mayhave the form of a simple apertured diaphragm.

In the case of pneumatic feeding devices having a plurality of feedinglines fed by one common compressed air source it is already known (DE-PSNo. 1 121 544) to have one single gas line leading from the compressedair source to each feeding line and to have a nozzle disposed in thisline for generating the velocity of sound. With the known constructiongeneration of the velocity of sound therefore serves a completelydifferent purpose in comparison with the feeding method according to theinvention, with which it is a question of effecting an even supply ofgas along an entire feeding line in order to achieve a seal flowfeeding.

It is advantageous to have the cross-sectional constriction formed by adosaging device, i.e. a dosaging device is disposed in each of the gaslines and is designed such that velocity of sound is generated at anover-critical pressure ratio, the velocity of the gas again beingreduced farther along the gas line and before it opens into the feedingline.

The invention therefore ensures that the amount of gas flowing througheach individual gas line is always exactly defined. Even if a plug formsin the feeding line, when the method according to the invention iscarried out gas still flows through all the gas lines into the feedingline, also through those gas lines which are in the area of the plug.The plug will thereby be dissolved again and feeding can besatisfactorily maintained.

Since the invention, for the first time, permits the amount of gassupplied to the feeding line through the individual gas lines to beexactly predetermined the invention also enables the known drop inpressure per section of feeding line to be taken into account and aneven conveying speed to be ensured despite the supply of carrier gasalong the feeding line: According to the invention the feeding line isdesigned such that its cross section widens in the direction of feedingin a predetermined manner.

In view of the even, shock-free and, if necessary, slow seal flowfeeding achieved according to the invention the abrasion on the walls ofthe feeding line and the material to be conveyed is reduced to aminimum. An additional advantage achieved by the invention is to be seenin the minimizing of the amounts of carrier gas which saves on energyand costs.

When compressed air is used as carrier gas the ratio of the pressurebefore the cross-sectional constriction to the pressure in the feedingline is preferably at least 2:1; a larger pressure ratio may, of course,be selected. Insofar as other gases (e.g. argon) are used as carrier gasa different minimum value for the over-critical pressure ratio will ofcourse apply--corresponding to the gas constants deviating from air.

The velocity of sound of the carrier gas aimed at in the gas lines is inany case ensured by the over-critical pressure ratio. The dosagingdevice, which may be, for example, a nozzle, an apertured diaphragm, acalibrated needle valve or the like, contributes substantially to thegeneration and maintenance of the velocity of sound in the gas lines. Acalibrated needle valve as dosaging device has the advantage that theamount of gas to be supplied may be varied within specified limits.

Additional features, advantages and details of the invention are givenin the attached claims and/or the following specification and theattached drawings of a preferred embodiment of a pneumatic feedingdevice according to the invention; the drawings show:

FIG. 1 a schematic illustration of the pneumatic feeding device;

FIG. 2 a section of the pneumatic feeding device, partially in sectionalview;

FIG. 3 a schematic diagrammatic illustration of the pressure andvelocity conditions within the feeding device according to FIG. 1 and

FIG. 4 an enlarged sectional view of the detail marked "X" in FIG. 2.

FIG. 1 shows a feeding line 10 comprising a plurality of partialsections 12 to 15, the diameter of which enlarges step by step in thedirection of feeding 11, for the pneumatic seal flow feeding of bulkgoods or powdery materials, heavy flowing masses, slurries or the like.With a view to the material to be conveyed the feeding line 10 issupplied by a feeding transmitter (not shown), into which the materialto be conveyed is fed in batches. A defined product feeding can therebytake place either due to the difference in pressure between feeding lineand feeding transmitter or due to a mechanical dosaging system, such asa screw conveyor or charging valve or by a blow dosaging slide. Two highpressure by-pass storages 16 and 17 are disposed parallel to the tubularfeeding line 10. The high pressure by-pass storages 16, 17 are designedwith a large volume and are supplied with pressure gas (e.g. compressedair) from a pressure gas source (not shown) which may also serve toadmit pressure gas into the feeding transmitter, or is independentthereof, via a pressure reducing device (not shown). The high pressureby-pass storages 16 and 17 serve to supply carrier gas to the feedingline 10. For this purpose a plurality of individual gas lines 18 issuefrom each of the high pressure by-pass storages 16, 17, these gas linesopening into the feeding line 10 at an angle of about 35° (cf. FIG. 2).The device described is designed such that when compressed air is usedthe pressure prevailing in the high pressure by-pass storages 16, 17 ishigher than that in the feeding line 10 by at least the factor of 2.This is a so-called over-critical pressure ratio which causes velocityof sound to be generated in the gas lines 18. For this purpose adosaging device 19 is disposed in each individual gas line 18. In theembodiment according to FIG. 2 an apertured diaphragm 20 serves asdosaging device, this apertured diaphragm being disposed at the end of afirst section 21 of the gas line. The apertured diaphragm 20 which issupported in the rearward direction by a reinforcement sleeve 25, has anarrow opening 26, the amount of gas flowing through being exactlydefined by its cross-sectional area. The second value for exactdefinition of the amount of gas flowing through the dosaging device isthe velocity of the gas. Since, as already mentioned above, anover-critical pressure ratio P₂ /P₁ prevails between the by-pass system16, 17 and the feeding line 10 (cf. also FIG. 3) the velocity of the gasin the apertured diaphragm is constant, i.e. equal to the velocity ofsound.

The sum of all the diaphragm cross sections, multiplied by the definedair or gas velocity (velocity of sound) results in the total amount ofcarrier air in the gas lines 18. The amount of air in the gas lines 18plus the amount of air in the pneumatic feeding transmitter (not shown)for the feeding line 10 results in the total air consumption.

Other dosaging devices, such as e.g. nozzles, calibrated needle valvesor the like, may be used instead of the apertured diaphragm 20, 26shown.

A filter 22 is connected to the outlet side of the apertured diaphragmin the feeding direction 27 of the gas in order to prevent any materialbeing conveyed penetrating into the gas line 18. The filter 22 isprovided in a second section 23 of the gas line. This has a considerablywider cross section than the opening 26 of the apertured diaphragm sothat the velocity of the gas at inlet 28 is again greatly reduced. Thiswill avoid abrasive wear on the inner walls of feeding line 10 as wellas within the goods to be conveyed. The almost tangential gas feeding inrespect of the direction of feeding 29 within the feeding line alsocontributes substantially towards minimizing abrasion, as shown clearlyin FIG. 2 (gas blow angle 35°).

The two line sections 21, 23 are connected with each other via a sealingscrew connection 24, the construction of which is illustrated in detailin FIG. 4 and which serves at the same time to fix the apertureddiaphragm 20 on the one hand and the filter 22 on the other. Accordingto FIG. 4 the screw connection 24 consists of a thread portion 30 withexternal thread 31, onto which a screw cap 32 is screwed. The screw cap32 has a central bore 33 which is penetrated by the portion 23 of thegas line. A cutting ring 35 is clamped between a conical bore 34 of thethread portion 30 and the end of the portion 23 of the gas lineextending into this bore. The cutting edge 36 of this cutting ring cutsinto the material of the portion 23 of the gas line under the radial andaxial pressure exerted by the screw cap and in this way provides asealing connection between the portions 23, 30. The sealing connectionbetween the other portion 21 of gas line 18 and the thread portion 30 isachieved in a similar way and also the connection of the gas line 18 tothe high pressure by-pass storage 16, 17. Here, too, a correspondingscrew connection is provided; this is shown in FIG. 2 under referencenumeral 37.

The diagram according to FIG. 3 shows that the feeding speed in theindividual sections 12 to 15 of the feeding line 10 remains essentiallyconstant due to the widening of their cross sections whereas pressure P₁steadily decreases along the feeding length L. Curve P₂ characterizesthe pressure in the high pressure by-pass storages 16 and 17. The highpressure by-pass storage or storages 16 or 17 ensure a defined supply ofgas over the entire length of the feeding line. The feeding of materialsis kept constant at each point along the feeding line system due touniform pressure ratios.

The pneumatic feeding shown and described may be used for customarypowdery and granulated products with the advantage of low energyrequirements as well as slight wear. A further possible application isin the feeding of difficult, abrasive, sticky, moist and sensitiveproducts. The feeding of such products was partially impossible withprevious pneumatic feeding systems. The system may also be used forfeeding coal in, for example, carbon pressure gasification plant.

We claim:
 1. Method for pneumatic feeding of materials to be conveyedalong a tubular feeding line supplied with conveying gas at leastsubstantially continually from at least one source of pressure gas via aplurality of gas lines discharging into the feeding line and spacedconsecutively apart from each other, comprising increasing the velocityof the conveying gas in each of the gas lines (18) to the velocity ofsound at a point (20) before the opening (28) whereby the amount of gasper unit of time flowing through said gas lines is independent of thepressure in said feeding line.
 2. Device for carrying out the methodaccording to claim 1, comprising a tubular feeding line, into which aplurality of gas lines open, said gas lines being spaced consecutivelyapart from each other and fed from at least one pressure gas source,characterized in that each gas line (18) has at a distance from itsopening (28) into the feeding line (10) a cross-sectional constriction(20), the throughflow cross-section of which being smaller than thethrough flow cross-section of the gas line downstream of saidconstriction, and that the pressure of the gas before thecross-sectional constriction is in overcritical ratio to the pressure inthe feeding line.
 3. Device according to claim 2, characterized in thatthe cross-sectional constriction (20) is formed by a dosaging device(19).
 4. Device according to claim 2 or 3, characterized in that whenair is used as carrier gas the ratio of the pressure before thecross-sectional constriction (20) to the pressure in the feeding line isat least 2:1.
 5. Device according to claim 2, characterized in that thecross-sectional constriction is designed as a nozzle.
 6. Deviceaccording to claim 2, characterized in that the cross-sectionalconstriction is designed as an apertured diaphragm (20).
 7. Deviceaccording to claim 2, characterized in that the cross-sectionalconstriction is formed by a dosaging device (19) having an adjustablyvariable throughflow passage.
 8. Device according to claim 7,characterized in that the dosaging device is designed as a, inparticular, calibrated needle valve.
 9. Device according to claim 2,characterized in that a carrier gas supply line (16, 17) runs adjacentto the feeding line, the gas lines (18) branching off from said supplyline.
 10. Device according to claim 2, characterized in that theindividual gas lines (18) each have a first line section (21) with adosaging device (20) disposed at its end and forming the cross-sectionalconstriction as well as a second line section (23) with a filter (22)disposed at its beginning and that the two line sections are detachablyconnected with each other by a sealing screw connection (24).
 11. Deviceaccording to claim 10, characterized in that the sealing screwconnection (24) serves to fix both the dosaging device (20) and thefilter (22).
 12. Device according to claim 2, characterized in that thepressure gas source (16, 17) is designed as a high pressure storage witha large storage volume in comparison with the total volume of all theindividual gas lines (18).
 13. Device according to claim 2, comprising apneumatic feeding transmitter for the material to be conveyed along thefeeding line, characterized in that the feeding transmitter on the onehand and the pressure gas source (16, 17) for the gas lines (18) on theother are connected to separate primary pressure-gas sources.
 14. Deviceaccording to claim 2, characterized in that the feeding transmitter andthe pressure-gas source (16, 17) for the gas lines (18) are connected toa common primary pressure-gas source, two branch lines issuing from saidsource, the one branch line leading directly to the pressure-gas source(16, 17) for the gas lines (18) and the second branch line leading via apressure reduction device to the feeding transmitter.
 15. Deviceaccording to claim 2, characterized in that the gas lines (18) open intothe feeding line (10) at an acute angle, preferably an angle ofapproximately 35 degrees, to the direction of feed (29).
 16. Deviceaccording to claim 2, characterized in that the gas lines (18) open intothe feeding line (10) in a turbulence blower having a plurality of blowapertures distributed over the circumference of the feeding line. 17.Device according to claim 2, characterized in that the cross section ofthe feeding line (10) widens in the direction of feed.
 18. Deviceaccording to claim 17, characterized in that the cross section of thefeeding line (10) widens in stages at or between the openings (28) ofthe gas lines (18).